The current theological hurricane in which we find ourselves (in both the society and the church) is complex, rendering a singular cause/effect description impossible. But like meteorologists, we can identify and explore particular factors that contribute to making the storm what it is.
One of the factors in the theological storm is the false allegation that “for more than 2000 years” there has been one orthodox belief.  The statement is used by fundamentalists to allege their beliefs express that very orthodoxy. And from their self-asserted position, they then go on to declare that those who believe differently than they do have denied the faith, or so seriously compromised the true faith, that light can no longer fellowship with darkness.
Historical theology exposes the allegation’s falsehood, revealing that for two thousand years the descriptive term for Christian theology is ‘diversity.’ We see this by looking at the creeds of Christendom themselves. Philip Schaff’s classic study is a multi-volume confirmation of this diversity. In the introduction, Schaff pointed to diversity by writing that the creeds “bring to light the various aspects and phases of revealed truth.”  “Various aspects.” Don’t miss that. It is Schaff’s way of recognizing that the creeds themselves bear witness to theological diversity within orthodoxy. A look at volume one of Schaff’s study explores diversity in detail. These main points emerge from that volume.
First, theological diversity gave rise to the creeds. Christians did not view faith through one lens in the two centuries after Jesus.  The grand ideas of faith were (and still are) too magnificent to be captured in any one interpretation. The documents leading up to the formulation of the creeds reveal diversity, within orthodoxy—not as an enemy of it. Using the creeds (and even less so the various attending doctrines related to them) to determine saints from heretics is not why the creeds came into existence in the first place. Their purpose was not to vilify differences, but to verify consensus. That’s why the creeds do not go into doctrinal detail about their affirmations.
Second, theological diversity is reflected in the creeds themselves. For example, in affirming Jesus the creeds select more than one phrase to describe him: “born of the virgin Mary”….”begotten not made”….”incarnate”….”Son of God”….”Son of Man”….”one Christ.” Each of these descriptions opens the way to more than one way of believing in him—ways that believers were using. The creeds themselves created their consensus by integrating the diverse ways Christians expressed their faith in Jesus.
Third, theological diversity continued after the creeds. This is one of Schaff’s main teachings in his study. The classic creeds did not end diversity, for they were not intended to do so. Instead, what we see in Christian history is the proliferation of diversity—within orthodoxy, not outside it or in opposition to it. Across the centuries, Christians have recognized that diversity enriches faith—sometimes as a “coat of many colors” and at other times through an “iron sharpens iron” dialog. 
Fourth, the continuing diversity of belief was not a way to deny earlier faith, but to apply it. This becomes clear in Schaff’s study when he looks at the statements of faith in Roman Catholicism, Orthodoxy, Protestantism, and the host of ecumenical affirmations that integrate the major traditions. The fact that theological statements did not cease after the creedal era is a testimony to the diversity which continued, finding expression in biblical, historic, systematic, and pastoral theologies, further detailed in their applications to specific periods of time, contexts, cultures, and countries.
Charles Wesley described the ongoing theological task as a means “to serve the present age,” and he (along with John and the early Methodists) said it was a charge they had to keep and a calling they had to fulfill, with all their might.  John expressed commitment to diversity when he abridged and edited the thirty-nine ‘Articles of Religion’ of the Church of England and sent the revision to the Methodists in America as they began their denomination in 1784.
Bottom line: Christians have not had one true faith “for more than 2000 years.” They have gazed at the masterpiece we call revelation and have borne witness to what they saw in a diversity of ways. There is not now, nor has there ever been, a mandated “one size fits all” orthodoxy. To allege that there is, is not to defend the faith, but rather to diminish it.
 I recently read this again in a statement written by a fundamentalist group. I have taken it directly from their own writing. It is one of their often-used allegations.
 Philip Schaff, ‘The Creeds of Christendom,’ 3 volumes (1877), and still available in multiple formats.
 The discovery of the Nag-Hammadi scrolls in 1945 has made this clear, shining new and brighter light on the theological diversity among the first (ante-Nicene) Christians. A recent book, ‘After Jesus, Before Christianity’ (HarperOne, 2021) looks at early Christian diversity in relation to the Roman empire and within the Christian community itself.
 E. Stanley Jones used the idea and practice of “the round table” in his ministry, writing in detail about it in his books, ‘The Christ at the Round Table’ (Abingdon Press, 1928) and ‘The Christ of Every Road’ (Abingdon Press, 1930).
 Charles Wesley’s hymn, “A Charge to Keep.” This commitment caused the Methodists to be caricatured as “enthusiasts” by the liberals and “latitudinarians” (we would say ‘pluralists’) by the conservatives. Ironically, truth is always a via media that is eschewed by extremists of all persuasions.
[This post also appears on Oboedire.]